Generally, automobiles or motorcycles are subject to vibration while running which leads to large variations in the liquid level within an oil tank, so that a liquid level detection switch may repeatedly go on and off in a chattering manner due to the variation, which may decrease the lifetime of the switch and may also distract the driver. Furthermore, the switch may be used in a wide temperature range, whereby a high reliability is required. A low manufacturing cost is also desired.
An explanation will be given of a conventional oil-level detection switch shown in FIG. 1 to 3, in which the driver is notified of a nead for oil when the engine oil is less than a certain amount. In the drawings, reference numeral 1 designates a pipe, the lower end of which has outwardly extending flanges receiving a support 2 of synthetic resin, the support 2 carries fixed contacts 3a and 3b comprised of a resilient metal mounted by rivets 5a and 5b respectively, and these contacts 3a and 3b form contacts 4a and 4b as shown in FIGS. 2 and 3. Wires 6a and 6b having at one end a connector 13 are inserted through the pipe 1 and soldered at the other ends to the rivets 5a and 5b, respectively.
A float 7 of foamed resin lower in specific gravity than oil has on at its lower end a movable ring-shaped contact 8 and is inserted so as to move vertically on the pipe 1. The liquid level S-S' is shown in FIG. 1, in which the float 7 is kept floating at an intermediate portion of the pipe 1.
At the upper end of the pipe 1 is provided a rubber casing 11 and a spacer 10 which are held by a ring 19 fitted into a groove 14, the casing 11 and spacer 10 being locked by a flange at the upper end of the pipe. Adhesive 12 is filled into a bore 15 provided at the center of casing 11 so as to fix the wires 6a L and 6b and close the upper opening to prevent oil leakage.
The flot 7 moves downward as the liquid level S-S' drops and, at its lower position, the movable contact 8 finally contacts the contacts 4a and 4b to make the fixed contacts 3a and 3b conductive to turn on the switch.
When oil is filled into the tank in this condition, the float 7 rises to automatically turn off the switch.
Chattering occurs in the conventional oil-level detection switch, however, because the liquid level S-S' is varying due to the vehicle's motion to vertically move the float 7 to repeat the connection and disconnection of the movable contact 8 and fixed contacts 3a and 3b even when the switch is on, which is not preferable for liquid level detection. The chattering will also occur even when the float 7 rises only slightly to turn off the switch.
Furthermore, the conventionl liquid level detection switch is structurally defective in that, caulking is frequently necessary because of the upper and lower flanges of the pipe 1, the fixed contacts 3a and 3b are riveted by rivets 5a and 5b, the wires 6a and 6b are soldered to the rivets, and a connector 13 needs to be used for the wires; thereby increasing the member of parts and manufacturing processes to result in a high manufacturing cost.